This research seeks to generate fundamental information on cell surface membrane changes of developing neurons. By utilizing the new technology of laser flow cytometry, a number of quantitative, single cell measurements will be made simultaneously on live neurons obtained from different regions of the central nervous system. Parameters to be measured include binding of biospecific probes such as fluorescent lectins which bind to specific cell surface carbohydrates, tetanus toxin, which binds to long chain gangliosides found specifically on neurons and measurements of cell size and nuclear/cytoplasmic ratio. These data obtained per cell will be correlated with the specific region of the central nervous system and the developmental stage of the animal. Neurons will also be stained by immunocytochemistry for protein markers before cytometric analysis so that the immunoreactive product and thus the specific subpopulation of neurons can be correlated wih levels of lectin and toxin binding per cell. Neurons from animals with known deficiencies such as the Brattleboro rat which contains magnocellular neurons lacking vasopressin will also be examined for cell surface membrane changes by the same criteria and will be compared to normal, developing neurons. Established neuronal cell lines will also be examined by flow cytometry for membrane changes specifically following "differentiation" by various agents. Lectins and toxin binding to differentiated cells will be quantified and measured simultaneously with stages of the cell cycle as determined by Hoechst dye-DNA fluorescence. Membrane fluidity of normal, developing neurons and differentiating neuronal cell lines will be determined by employing flow cytometric analysis of specific membrane probes. Results of this proposed research will help us understand neuronal recognition which occurs at precise times in development and may help us to explain certain disease states in which specific neurons lack proper "input" from appropriate regions.